At the Barnham excavation, there are two areas where digging has actively taken place in recent years; Area IV/VI, a cobbled palaeo-lakeshore, and Area III, roughly in the middle of the former lake. We know that the latter area used to be a lake, because of the fine sediments characteristic of fluvial deposits, but also because of the high number of fish bones, as described by Tess Bakker in a previous blog. From these fish species, we can determine whether the water was fresh or perhaps brackish, whether it was flowing or still standing and many more aspects. However, there are also features to the waterbody we can only study by looking at the objects that do not naturally belong in the water, but somehow ended up at the bottom of the lake. One of these features is the direction of the lake’s current. By measuring the direction in which elongated objects are oriented, we can reconstruct the axis and direction of the current. But how do we measure orientation and thereafter determine the direction of the current?
First of all, elongated objects can be bones and artefacts, but also unworked flint, of which the longest axis, referred to as ‘a-axis’, is 1.5 times larger than the ‘b-axis’, which is perpendicular to the ‘a-axis’. Holding a compass with a rectangular outline parallel to the object’s most inclined axis, we can read the object’s orientation relative to the magnetic north off the compass’ dial.
Secondly, the orientation data will be plotted in a so-called ‘Rose-diagram’ after all measurements have been digitalized. The plotted data should show a concentration in a general direction (e.g. ‘north by northeast’ or ‘southwest’), which will be the direction from which the water was flowing. The measurements point to the source of the flowing water, since the highest end of objects will be forced to point downstream by the moving water, resulting in the object to dip in the direction of the water’s source. However, several processes can influence the precision of our measurements. These can be large animals drinking from the lake and by accident walking on the deposited objects, affecting their orientation and dip, a process called ‘trampling’, but it is also possible that some of the objects we find were not transported by water, but entered the lake’s sediments because an animal died in shallow areas of the lake, or early hominins discarding bones of butchered animals and/ or threw rocks in a lake for reasons we can only speculate about.
To differentiate objects deposited by flowing water from intrusions, we measure the dip of the objects with a clinometer. If items are positioned vertically, they are more likely to be unaffected by the current and hence not very informative for our main research question. This way we can make a general distinction and make our results more precise and reliable.
Although we presume that the objects in the lake did not leave behind broken marriages during their travels, but in order to learn more about our palaeo-lake we still ask them the same question Cotton Eye Joe was asked: “Where did you come from and where did you go?”